1. Field of the Invention
The present invention relates to sealing machines for bales or packages, such as high quality rubber crumbs or chips.
2. Description of the Related Art
A considerable number of types of packages or cartons are wrapped and then heat sealed into a protective synthetic resin film for shipment. So far as is known, the heat sealing has been done by a set of elongate heat elements formed in the horizontal outline or configuration of the package, usually a rectangle or square. An example of such an elongate heat element or rod is a product known as a Calrod.RTM. sold by General Electric Company. The rod received a flow of electrical current through it and generated heat to partially melt edges of the film together to seal the film into a protective film wrap over the box or product. The heat rod was usually enclosed in a non-adhesive protective cover, such as that sold by E. I. duPont de Nemours and Company under the trademark Teflon.RTM., to prevent the film from sticking to heat element.
For example, high quality rubber is prepared in a process that forms small chips or clumps, often termed crumbs, of relatively soft, pliable rubber. The resultant rubber is typically referred to as crumb rubber. Examples of such types of crumb rubber are those provided under the trademarks Budene.RTM., Natsyn.RTM. and Chemigum.RTM. of Goodyear Tire & Rubber Company. It has been typical to form the rubber crumbs into bales for ease of handling, storage and shipment. U.S. patent application Ser. No. 08/873,388, filed Jun. 11, 1997 now U.S. Pat. No. 5,870,951, of which applicant is the inventor, is one type of such a baling machine.
After the bale of rubber particles is formed, the bales are then wrapped within a protective synthetic resin film. The protective synthetic resin film prevented the relatively soft bales from sticking together when stacked for storage or shipment. The film wrapping also maintained the integrity of the bale during handling, storage and shipment. It was also desirable that this rubber after being made be kept free from contamination by metal particles, dirt, liquids, or other contaminants. The film wrapping was then heat sealed along seams about the rubber bale to enclose the rubber to prevent sticking, maintain integrity of the bale and also keep out contaminants. Typically, a set of heating element rods or blades in a sealing machine or press of the type described above gripped portions of the film and heated it to form a sealed seam.
There have, however, been problems with these heat sealing elements and assemblies. The temperature of the heat sealing assemblies fluctuated along their length, and in a non-uniform manner. Where the temperature was uneven along the heat sealing element, either cold spots or hot spots could result at certain locations. Where there were cold spots, the film edges of the seam often did not seal, or only partially sealed. This left openings along the seam where rubber or other package contents would be exposed and possibly adhere to adjacent bales or other objects or where contaminants might enter.
If the temperature of the heating elements was raised to avoid cold spots, the service life of the heating element was reduced because of increased temperature. Further, certain areas along the length of the heating elements could reach too high a temperature and cause hot spots. At hot spots, the heat could become high enough to burn holes through the film, again causing exposure of the contents with sticking problems and also the risk of contamination of the contents of the bale or package.